This invention relates to a method for conditioning a subterranean formation containing clay particles creating adverse permeability effects around a well bore communicating from the surface of the earth to the formation in order to increase the recovery of heavy viscous hydrocarbon materials, such as petroleum crude oil or synthetic fuels. The presence of clay particles may create adverse permeability effects in the formation and particularly around the well bore by swelling if water-sensitive clays, particle plugging by dispersal of clay fines or by particle invasion of such fines. Such effects reduce permeability of the formation both to fluids injected for stimulation of production of viscous hydrocarbons and to the production of the hydrocarbons themselves.
There are many methods known in the art for injecting thermal energy into a formation for the purpose of reducing the viscosity of heavy viscous petroleum crude oil so that it may be recovered. Such methods are usually classified as "thermal drive", "single well thermal injection" or the like. Thermal drive processes basically involve injecting thermal energy, usually from steam boilers or in situ combustion, into an oil-bearing formation by means of an injection well, driving the petroleum towards one or more adjacent producing wells and recovering the petroleum through the producing wells. Single well thermal injection processes usually involve injecting thermal energy into the oil-bearing formation by means of an injection well and subsequently withdrawing the resulting heated petroleum through the same well. Such single well thermal injection processes are also commonly referred to as "huff-and-puff" processes. There are, of course, many modified versions of these basic techniques known in the art which employ a wide variety of thermal energy agents, such as hot water, in situ combustion gases, steam, heated condensable and non-condensable gases, and the like.
Although many thermal injection methods have been useful under certain conditions, there are many formations known to contain large volumes of heavy viscous petroleum from which the petroleum has not been economically and efficiently recovered by the employment of any known thermal injection technique. By way of example, there are many formations located throughout the United States, particularly throughout southern Illinois, western Missouri, southeastern Oklahoma, and southern Kansas, saturated with heavy viscous crudes, e.g., having viscosities greater than 200 centipoises and/or API gravities below about 22.degree. (both at 60.degree. F.), which have not been recovered in economic quantities by employment of conventional recovery techniques. Additionally, previous attempts to increase the recovery of such heavy crudes from such formations by the employment of known thermal injection processes, especially direct single well steam injection, have been substantially unsuccessful. As known, one of the primary problems in attempting to recover such viscous crudes from such formations is that the formations have such low relative permeabilities to oil and water that thermal energy cannot be injected into the formations at economic injection rates. In fact, there are many formations which have such low relative permeabilities to oil and water that they will not accept sufficient quantities of thermal energy by the employment of known injection processes at any injection rate.
A recent patent discloses a method for enhancing petroleum production in such formation. For example, U.S. Pat. No. 3,993,135 discloses a method comprising initially heating a well bore penetrating the formation and surrounding subterranean strata with a thermal vapor stream containing combustion gases and superheated steam until sufficient heat is imparted thereto to permit the thermal vapor stream to be injected into the formation at a desired high injection rate. The well bore and surrounding strata are heated by continuously injecting the thermal vapor stream into the well and simultaneously venting a portion of the vapor stream from the well at the surface to remove condensed liquids formed from while heating the well bore and formation face. The heated fluid is then injected directly into the formation at a desired high injection rate until the formation and viscous petroleum contained therein are heated and the viscosity of the hydrocarbons is reduced. Injection is then discontinued and the heated crude is produced through the well. Surprisingly, and contrary to prior attempts, a formation having low relative permeabilities to water and oil will readily accept a thermal vapor stream containing steam at high injection rates when the heated fluid containing steam is injected in accordance with the process of U.S. Pat. No. 3,993,135. U.S. Pat. No. 4,118,923 describes apparatus particularly suited for generating a thermal vapor stream for use in the described method.
Best results are obtained with the above process when the heated fluid is injected at the maximum injection rate possible so as to impart heat to the formation as rapidly as possible. But it has now been found that the above process cannot be applied to maximum efficiency in those formations which clay particles which cause adverse permeability effects by swelling upon contact with water or being of such fine particle size that the particles migrate through the formation ultimately plugging the formation. Injection of a thermal vapor stream as described in U.S. Pat. No. 3,993,135 causes the fine particles to migrate through the formation to ultimately plug the formation. Where the clays are water-sensitive, swelling occurs. Such swelling lowers the already low permeability of such formations which lowers, for practical purposes flow of the thermal vapor stream into such formations and greatly impeds the recovery of petroleum from such wells. Additionally, when a continuous thermal drive technique is employed the presence of such clays within the formation around the drive well impeds the ability to drive the petroleum crudes from the field through the use of the injection well. Examples of such clays which adversely affect the permeability of such formation include, for example, illite, smectite, bentonite and montmorillonite.
Traditional treatment of such formations with hydrogen fluoride to dissolve the clay or with clay stabilizers has proved unsuccessful, partly because of the difficulty of removing carbonaneous materials, such as oil, from the clay particles. The coating of crude oil prevents the hydrogen fluoride from attacking and dissolving the clays. This result is partly because hydrogen fluoride reacts with calcium, magnesium and other metals contained in the formation to form insoluble metal fluoride salts which are deposited within the pores of the formation to further limit its permeability. Attempts to solve this problem, such as described in U.S. Pat. No. 4,136,739 illustrate the difficulty in treating formations with hydrofluoric acid and hydrochloric acid to solve the problems created by clay particles which adversely effect the permeability of oil-bearing formation. These problems are compounded when heavy viscous hydrocarbons are present in the formation. Further, conventional acidizing with hydrogen fluoride is very corrosive and causes considerable damage to the well bore.
Treatment similar to that described in the prior art was attempted where a liquid hydrocarbon, in this case diesel fuel, was injected into the formation to attempt to remove heavy viscous crude in the presence of such clay particles to make them susceptible to treatment with hydrofluoric acid failed. No increased permeability was noticed.